There are distinct gaps in our understanding of the link between obesity and/or fat distribution and increased disease risk in adolescent children. We propose a 5-year longitudinal study to examine the temporal relationships between changes in body fat, body fat pattern, insulin sensitivity, lipd profile, physical activity, and sex hormones during adolescent growth. We will use state-of-the-art techniques for measuring total body fat (4-compartment model), body fat pattern (dual energy X-ray absorptiometry, computed tomography), physical activity (combination of doubly labeled water and indirect calorimetry), and whole-body insulin sensitivity (Bergman Minimal model). We will examine blood pressure and circulation lipid and lipoprotein levels as risk factors for cardiovascular disease, and fasting indulin and insulin sensitivity as risk factors for non-insulin dependent diabetes mellitus. We propose to study Caucasian and African American adolescents because these groups are at increased risk of obesity and related diseases and have not been thoroughly examined. Preliminary data and recent publications from other investigators support the concept that accumulation of body fat in the intra- abdominal region begins to occur before and during adolescence. Moreover, these data provide evidence that the relationship between obesity and disease risk in adolescents may be explained by accumulation of intra-abdominal adipose tissue (IAAT). Thus, we propose to examine the following hypotheses: 1) The relationship between obesity and disease risk in Caucasian and African American adolescents is due specifically to the accumulation of IAAT; 2) Physical inactivity, total body fat, and sex hormone levels contribute to the development of IAAT during adolescence, which leads to the development of insulin resistance which in turn leads to the development of dyslipidemia. The strength of these cause and effect relationships will not be significantly influenced by ethnicity, or gender; and ,3) IAAT can be accurately predicted from anthropometry, and more accurate equations can be developed by inclusion of total abdominal fat by dual energy X-ray absorptiometry. Our unifying hypothesis is that the development of IAAT during adolescence is the specific cause of increased risk of disease resulting from obesity. This longitudinal study will add to our understanding of the etiology of obesity and the emergence of different body fat patterns during adolescent development. The study will yield substantial information of the mechanism(s) relating obesity to increased disease risk in Caucasian and African American adolescents, and this information will be useful for the design of prevention and intervention programs aimed at reducing long term risk of disease.